The malaria infection is initiated by mosquito injection of sporozoites into a mammalian host. Evidence shows that sporozoites are injected by mosquitoes into avascular portions of the skin rather than directly into blood. Sporozoites must then travel to blood vessels to induce an infection. Broad, long-term objectives of this project are to obtain a better understanding of the dynamics of mosquito injection of sporozoites in relation to 2 significant health issues: immunity to sporozoites and sensitization to mosquito bite. Sporozoites deposited in avascular skin tissue by mosquitoes are exposed to antibodies and other host defense mechanisms for at least several minutes before they reach the blood. Thus, sporozoites migrating through the skin may be killed by host cells or by anti-sporozoite antibodies. Furthermore, the immediate hypersensitivity skin reaction to mosquito bite may modulate sporozoite migration. Specific aims are to 1) determine the kinetics of Plasmodium sporozoite passage from mosquito proboscis to blood. 2) Investigate how vaccination against sporozoites influences the successful migration of mosquito deposited sporozoites from skin to blood. 3) Determine whether an immediate hypersensitive cutaneous reaction to mosquitoes influences migration of mosquito-deposited sporozoites from skin to blood. Research design and methods will include: 1) Quantitative and confocal microscopy studies of sequential timed biopsy specimens of the skin will make counts of fluorescent sporozoites injected into skin by mosquitoes, and the interactions of sporozoites with cells of the skin. 2) Intravital microscopy studies with fluorescent sporozoites will measure deposition and behavior of sporozoites in mouse skin and the clearance rate of these sporozoites from the skin. For this investigation, mice immunized against sporozoites will be studied to assess the effects of anti-sporozoite antibodies on the kinetics of sporozoite passage from skin to blood and mice immunized to mosquito bite will be studied to assess the effects of immediate cutaneous hypersensitivity on the kinetics of sporozoite passage from skin to blood.